Since absorption spectra of substances relating to living bodies, health, environments and the like are located in a near-infrared to infrared wavelength region, photodiodes having sensitivity in this wavelength region have been developed. For example, NON PATENT LITERATURE 1 proposes a photodiode including an absorption layer having an InGaAs/GaAsSb type-II multiple quantum well (MQW) structure on an InP substrate, as a device to improve sensitivity on the long wavelength side of the near-infrared region. This photodiode is a mesa-type single-pixel photodiode, and includes an InGaAs buffer disposed on the InP substrate, and the InGaAs/GaAsSb type-II multiple quantum well structure disposed on the buffer. This photodiode has a cutoff wavelength of 2.39 μm, and sensitivity characteristics at wavelengths from 1.7 μm to 2.7 μm are shown.
Meanwhile, a photodiode including an array of a plurality of pixels (absorption portions) is used in image pickup devices and the like. PATENT LITERATURE 1 proposes a planar photodiode in which an array of pixels is formed by introducing impurities by selective diffusion. In the photodiode, the above-mentioned InGaAs/GaAsSb type II multiple quantum well structure is used, and a semiconductor layered structure is appropriately modified to prevent the multiple quantum well structure from being deteriorated by the impurities. By using this semiconductor layered structure, it is possible to obtain a photodiode including arrayed pixels having sensitivity in the near-infrared to infrared region.
Although the above-mentioned image pickup devices and the like are desired to provide high-definition images, it has been known that the above-mentioned near-infrared-to-infrared photodiode has degradation of image quality caused by dark current. For example, in NON PATENT LITERATURE 1, since there are multiple causes of dark current, study to theoretically know the degree of each cause has been executed.